This invention relates to a method and apparatus for mounting components and more particularly to an improved method and apparatus for more precisely picking up components to be mounted on a substrate.
A wide variety of types of apparatus have been proposed for picking up small components such as integrated circuits, resistors or the like, and mounting these components at an accurate location on a substrate. The components are normally picked up by a pick-up device such as a vacuum pickup nozzle from a feeder station. When the components are picked up, their orientation relative to the pick-up device cannot be accurately controlled so as to insure precision mounting. Therefore, it has been proposed to provide various ways in which the orientation of the component, as picked up by the pick-up device, is determined, and then the mounting position is corrected to accommodate errors in the pick-up location.
The co-pending application of the inventor hereof, entitled "Method For Mounting Components And An Apparatus Therefor," Ser. No. 08/073,741, filed Jun. 8, 1993, and assigned to the assignee hereof now issued as U.S. Pat. No. 5,384,956 on Jan. 31, 1995, discloses a method whereby optically it is possible to determine the orientation of a component picked up by the pick-up device by rotating the component and measuring the projected length of the component in two (2) angular positions. From these measurements, the actual location of the component can accurately be determined and the corrective factors calculated.
Typically, the optical detector will raise components to a pre-determined recognition height. Unfortunately, not all components are shaped such that an accurate determination of the component location can not be determined at the same recognition height. In addition, the parameters measured to determine the location of the component may include noise. Such noise may result from debris, loose wires or, even, a polished portion of the component itself causing the light beams to be reflected in a misleading manner. As a result of these difficulties properly picked up components may be discarded and improperly picked up components may be improperly mounted.